The invention relates to a bucket tappet for an internal combustion engine having a tappet housing with a hollow cylindrical bucket skirt and a bucket base which closes the bucket skirt on one side and on which the bucket skirt is formed by cold forming a steel blank without cutting, wherein the outside of the bucket base is used as a contact surface for a cam of the internal combustion engine for transferring a stroke movement to the bucket tappet and for which the outside of the bucket skirt is used as a contact surface for a guide hole of the internal combustion engine supporting the bucket tappet in the stroke direction.
Such bucket tappets are used in gas exchange valve trains of internal combustion engines to transfer the cam lifting of a cam to a camshaft in an opening movement of the associated gas exchange valve. There is also the ability to use the bucket tappet as a tapping element for the cams of a fuel injection pump to transfer the lifting of the pump cam to the piston of the injection pump. Each case involves a mechanically strongly loaded component that must sufficiently withstand, on one hand, the Hertzian pressure forces occurring in the cam contact area with low wear and is to be sufficiently supported, on the other hand, in a guide hole with low wear and low noise.
For a long time, bucket tappets that are suitable for large-scale production have already used steel tappet housings that are cold formed without cutting and are then heat treated for increasing the hardness of all contact surfaces. The final contour of the tappet housing generated by cutting is typically produced in a grinding process in which the outside of the bucket skirt, that is, the guide contact surface of the bucket tappet, is finished to the tolerance dimension required for the longitudinal guide of the bucket tappet and the outside of the bucket base, that is, the cam contact surface, is finished to the surface geometry required for the cam contact while reducing the surface roughness.
From DE 10 2011 076 410 A1, a bucket tappet and a method for its production are known. The metal tappet housing is produced by a cold forming process without cutting, then heat-treated, and finally the outside of the bucket skirt is ground to the required dimension. The surface geometry required for the cam contact is achieved by a polishing and/or lapping process. Then a diamond-like carbon (DLC) coating is applied that is then reprocessed mechanically by brushing. The brushing process is constructed so that each section of the surface to be processed is processed uniformly with respect to processing intensity and also the relative movement between the bucket tappet and the brushing tool, in particular, without preferring any certain direction, so that an isotropic, wear-optimized, and friction-optimized surface structure is produced.